This invention relates to a drill for drilling a substantially cylindrical hole in a workpiece. More particularly, the invention relates to a drill of the same general type as the drill disclosed in Shallenberger, Jr. U.S. Pat. No. 3,963,365. In that drill, two cutters in the form of indexable cutting inserts are supported by a drill body which is adapted to be rotated about an axis coinciding with the axis of the hole. When the drill body is rotated, one of the inserts cuts the central portion of the hole while the other insert cuts the peripheral portion of the hole. Each insert may be periodically indexed and/or inverted to bring a fresh cutting edge into active cutting position and, when all of the available edges have been worn, the insert may be removed from the drill body and replaced with a new insert.
The drill disclosed in the Shallenberger, Jr. patent performs admirably when drilling holes of relatively large diameter. The drill does not, however, readily lend itself to drilling holes of comparatively small diameter because of the physical impracticality of fitting two inserts of cutters into a relatively small hole. While drills with a single cutter do exist, the cutter of such a drill does, to the best of my knowledge, form the hole by making a single cut which is equal in radial length to the radius of the hole. In other words, the cutter cuts away a chip and forms the hole by sweeping through a path which extends radially from the center of the hole to the wall thereof.